1. Field of the Invention
The present invention generally relates to a width adjusting device for a paper web, which adjusts the width of the paper web for a printing system prior to a printing section. More particularly, the present invention relates to a rotary lithographic press which is equipped with at least one of the width adjusting device and a plurality of printing sections through which the paper web is successively travelled to be printed.
2. Description of the Prior Art
A typical conventional rotary lithographic press adapted for a multi-color printing system is, for example shown in FIG. 22 which is a schematically elevational view. This conventional lithographic printing system comprises a plurality of printing sections P, each of which includes two pairs of a combination of a plate cylinder PC and a blanket cylinder BC. The blanket cylinders BC of each printing section P are vertically arranged to be in contact with each other. In this conventional printing system, four sets of the printing sections P are horizontally arranged in parallel as shown in FIG. 22. A paper web W is also horizontally travelled through the printing sections in which the paper web W is successively passed between the pairs of blanket cylinders BC, BC to print both sides of the paper web W.
Another conventional rotary lithographic press or a multi-color printing system is shown in FIG. 23. In this drawing, four printing sets, each composed of a plate cylinder PC and a blanket cylinder BC are radially arranged about an impression cylinder IC as a common center cylinder. The blanket cylinders BC are respectively in contact with the impression cylinder IC to form printing sections P. A paper web W is travelled along the circumference of the impression cylinder IC so that the paper web W is successively passed through the four printing sections P defined between the blanket cylinders BC and the impression cylinder IC to print one side of the paper web W.
In recent years, many newspaper publishers have progressed to bring newspaper in multi-color ink and thus demand the capability of color printing on many pages at a high speed in a limited printing space.
In order to satisfy such demands, another conventional rotary lithographic press for a color printing system has been proposed as shown in FIG. 24 and FIG. 25. In this printing system, each printing section P includes two sets of a blanket cylinder BC and a plate cylinder PC which are symmetrically arranged so as to bring the blanket cylinders BC into contact with each other. A paper web W is vertically travelled through the four printing sections P to print both sides of the paper web W in the same manner as the above described systems. This type of printing system is, for example, shown in "IFRA Newspaper Techniques English Edition", pp.64 to pp.73; April, 1988 published by INCA-FIEJ Research Association.
Paper webs used in various printing systems are generally produced in such a manner that pulp fibers are mechanically cut and broken into fine particles, dispersed in water, dehydrated and dried, and finally adhered by hydrogen-bond to form paper in a web or sheet figure. Under moist conditions, each pulp fiber tends to extend a little less than 1 percent in length and 20 to 30 percent in width. Thus the size of the paper web is increased, both longitudinally and laterally by a dampening and/or watering process. Most pulp fibers of general mechanically produced paper webs are orientated in the longitudinal direction of the paper web, so that paper webs are remarkably extended in their width.
In a specific lithographic printing system which employs a dampening or watering operation in printing, a paper web is swelled by the water supplied during the dampening operation. Therefore the image and lines printed on the paper web are also deformed in response to the swell of the paper web. In printing systems that include at least two lithographic printing sections each associated with dampening means to successively print color images on the same paper web, the printed images or lines formed by the first printing section are not correctly accorded with the images or lines formed by the second and later printing sections. Accordingly, this will produce printed materials of poor quality.